Simplify 50 move rule dampening
Refactor the logic of 50 move rule dampening by removing a constant.
Passed non-regression STC:
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 35232 W: 9214 L: 8992 D: 17026
Ptnml(0-2): 114, 4081, 8999, 4313, 109
https://tests.stockfishchess.org/tests/view/665a329013d08af3c1725610
Passed non-regression LTC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 38406 W: 9732 L: 9530 D: 19144
Ptnml(0-2): 14, 4132, 10708, 4336, 13
https://tests.stockfishchess.org/tests/view/665a370913d08af3c1725651
https://github.com/official-stockfish/Stockfish/pull/5327
Bench: 1059739